1. Field of the Invention
The present invention relates to an optical film, a process for producing an optical film, a polarizer, and an image display device.
2. Description of the Related Art
Recently, a liquid crystal display device has been widely used for a liquid crystal television, and a liquid crystal panel of a personal computer, a mobile phone, and a digital camera, and the like. In general, the liquid crystal display device includes a liquid crystal panel member having polarizers on both sides of a liquid crystal cell, and controls light from a backlight member by the liquid crystal panel member, and thus performs display. Here, the polarizer is formed of a polarizing element and protective films on both sides of the polarizing element, a general polarizing element is obtained by dyeing a stretched polyvinyl alcohol (PVA)-based film with iodine or a dichroic dye, and a cellulose ester film or the like is used as the protective film.
Recently, the liquid crystal display device has been relentlessly required to have high quality, versatile application, and durability. For example, when the liquid crystal display device is used in outdoor applications, stability with respect to an environmental change is required, and an optical film such as the protective film for a polarizer described above or an optical compensation film used in the liquid crystal display device is also required to suppress a change in dimension or optical properties with respect to a change in temperature or humidity. As a problem of the liquid crystal display device which is exposed to a high temperature and high humidity environment, warping of the liquid crystal cell of the liquid crystal display device, and the occurrence of display unevenness are included, and it is considered that this is because a shrinkage difference is generated between the polarizers on a front surface and a back surface of the liquid crystal cell of the liquid crystal display device due to a change in temperature and humidity of the use environment of the polarizer and the optical film configuring the polarizer, the balance is broken, and thus the liquid crystal cell is warped, and four corners or four sides of the liquid crystal cell are in contact with a housing or member on the back surface side, and thus the display unevenness occurs. For this reason, the protective film of the polarizer, the optical compensation film, and the like have been required to improve humidity dependency resistance and moisture-heat resistance, and in order to drastically improve these properties, the optical film on an outermost surface of the polarizer on a visible side has been required to reduce moisture permeability.
In WO2009/047924A, in order to provide an optical film having high transparency, low hygroscopicity, high heat resistance, and high mechanical strength, an optical film is disclosed in which a large amount of acrylic resin such as polymethyl methacrylate (PMMA) is added to cellulose ester.
On the other hand, a film has also been known in which a layer of low moisture permeability is disposed on a light transmissive support body. For example, in JP2006-83225A, a film is disclosed in which a layer of low moisture permeability formed of a composition containing a compound having an alicyclic hydrocarbon group and two or more ethylenically unsaturated double bond groups in a molecule is disposed on a light transmissive support body of cellulose acylate having a film thickness of 80 μm, and moisture permeability measured on the basis of JIS Z 0208 under an atmosphere of 60° C. and a relative humidity of 95% is approximately 610 g/m2/day to 1000 g/m2/day.
In addition, in JP2008-230036A, a film is disclosed in which a layer of low moisture permeability containing a resin having a repeating unit derived from a chlorine-containing vinyl monomer is disposed on a light transmissive support body of cellulose acylate having a film thickness of 80 μm.